McGeouch-Flaherty, Carrie-Anne (2011) Proton assisted dissolution of the dental hard tissue enamel as a non-bacterial process. PhD thesis, University of Warwick.

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Abstract

The overall aim of this thesis was to examine the kinetics of proton-promoted dissolution of
the dental hard tissue enamel as a non-bacterial process and the evaluation of inhibitors with
the intent of minimising the dissolution process and effectively protecting the surface.
A novel approach was taken, utilising scanning electrochemical microscopy (SECM) to
galvanostatically generate controllable and well defined proton fluxes in defined areas of the
surface. The resulting etch pits formed on the surface were characterised by optical
microscopy and white light interferometry (WLI), which quantitatively determined etch pit
dimensions. A theoretical finite element model (FEM) was used to elucidate the kinetics of
dissolution based upon the analysis of the shape and dimensions of etch pits produced. A
heterogeneous rate constant of dissolution of 0.08 ± 0.04 cm s-1 was attributed to untreated
enamel, whereas 2 min treatment with 1000 ppm sodium fluoride (NaF) decreased this rate
constant slightly to 0.05 ± 0.03 cm s-1. The impact of fluoride on the rate of proton attack
was evident from the formation of shallower broader etch pits.
In relation to both acid erosion and caries, the two most relevant acids pertinent to enamel
dissolution are citric acid and lactic acid. These acids were investigated by protonating their
respective sodium salts in-situ to produce localised weak acid directly under the probe tip.
This permitted the surrounding enamel sample to remain largely unaltered giving a true
surface for comparison, whilst allowing evaluation of the kinetics in the presence of each
weak acid. Etching in the presence of lactic acid, showed a surface controlled process with a
rate constant of 0.1 ± 0.03 cm s-1. Etching in the presence of the triprotic citric acid, also
yielded a surface controlled process with a rate constant of 0.35 ± 2.6 cm s-1.
Calcite was also investigated using SECM, WLI and FEM to validate the use of these
techniques. The kinetic data extrapolated was comparable to rate constants found in literature,
confirming the validity of these methods. In this case, a novel approach was the use of
experimental data to parameterise the finite element model directly.
Confocal laser scanning microscopy (CLSM) coupled with SECM was used to visualise
proton fluxes from the tip of the UME. This allowed, not only, correlation of the current
applied to the probe tip with the pH, but also quantitative data on the spread of protons across
a particular surface. Rate constants found for untreated and fluoride-treated enamel were
comparable to those found in SECM etching, however, zinc ion treatment proved to result in
much greater inhibition of dissolution than fluoride.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry R Medicine > RK Dentistry
Library of Congress Subject Headings (LCSH):	Dental enamel, Protons -- Physiological effect, Fluorides -- Physiological effect, Dental caries -- Prevention
Official Date:	September 2011
Dates:	Date Event September 2011 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Unwin, Patrick R. ; Parkinson, Charles
Extent:	xxvii, 223 leaves : ill., charts
Language:	eng

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